Metathesis is a catalytic reaction that involves the interchange of alkylidene units among compounds containing one or more double bonds (e.g., olefinic compounds) via the formation and cleavage of the carbon-carbon double bonds. Metathesis may occur between two like molecules (often referred to as self-metathesis) and/or it may occur between two different molecules (often referred to as cross-metathesis). Self-metathesis may be represented schematically as shown in Equation I.R1—CH═CH—R2+R1—CH═CH—R2R1—CH═CH—R1+R2—CH═CH—R2  (I)
wherein R1 and R2 are organic groups.
Cross-metathesis may be represented schematically as shown in Equation II.2R1—CH═CH—R2+2R3—CH═CH—R4R1—CH═CH—R3+R1—CH═CH—R4+R2—CH═CH—R3+R2—CH═CH—R4  (II)
wherein R1, R2, R3, and R4 are organic groups.
In recent years, there has been an increased demand for environmentally friendly techniques for manufacturing materials typically derived from petroleum sources. For example, researchers have been studying the feasibility of manufacturing biofuels, waxes, plastics, and the like, using natural oil feedstocks, such as vegetable and seed-based oils. In one non-limiting example, metathesis catalysts are used to manufacture candle wax, as described in WO 2006/076364, which is herein incorporated by reference in its entirety. Metathesis reactions involving natural oil feedstocks offer promising solutions for today and for the future.
Natural oil feedstocks of interest include non-limiting examples such as natural oils (e.g., vegetable oils, fish oil, animal fats) and derivatives of natural oils, such as fatty acids and fatty acid alkyl (e.g., methyl) esters. These feedstocks may be converted into industrially useful chemicals (e.g., waxes, plastics, cosmetics, biofuels, etc.) by any number of different metathesis reactions. Significant reaction classes include, as non-limiting examples, self-metathesis, cross-metathesis with olefins, and ring-opening metathesis reactions. Representative non-limiting examples of useful metathesis catalysts are provided below. Metathesis catalysts can be expensive and, therefore, it is desirable to improve the efficiency of the metathesis catalyst.
In certain instances, metathesis of natural oil feedstocks may provide a useful way to make chemical intermediates that may be difficult to make by other means. Or, in some other instances, metathesis of natural oil feedstocks may provide a useful way to make “green” alternatives to existing compounds or materials. Therefore, there is a continuing need to develop processes and systems that employ natural oil metathesis to make commercially and/or technically useful compounds and materials.